Solid-state imagers are finding increased use in cameras for detecting radiant energy in the visible and infrared light range due to their long life, low power consumption and small size, as compared with conventional image pick-up tubes. Solid-state imagers include an imaging area comprising an array of discrete photosensitive picture elements (pixels) for responding to light from a scene. Typically, solid-state imagers which are suitable for use in television cameras, such as the x-y addressed MOS field-effect transistor type or the self-scanned CTD (charge transfer device) type, have up to 200,000 pixels. Defects occur in solid-state imagers because of random non-uniformities in semiconductor substrate material from which the solid-state imagers are fabricated, and impurities and/or imperfections introduced during the manufacturing process. For example, one type of imaging response characteristic for a solid-state imager is dark current response. It is well known that semiconductor devices exhibit a certain amount of leakage current. In a solid-state imager, the leakage current may result in the collection of a charge in a pixel even in the absence of photo-excitation and is known as the dark current response. When solid-state imagers are used in television cameras, the dark current (nonimage-representative) response of each pixel must be relatively low as compared to its image-representative photoresponse so as to allow television signals to be generated with an acceptable signal-to-noise ratio. However, if the dark current response for a particular pixel is higher than the average level of its surrounding pixels, it will show up as a "white spot" defect in the generated television signal. Impurities and/or imperfections introduced during the manufacturing process of the imager can also cause a "black spot" defect in a television signal. Because of defects, the manufacturing yield of solid-state imagers having a large number of pixels, such as those suitable for high quality television cameras, may be quite low. Thus, each imager must be carefully tested to screen out those with defects and a high cost is associated with the relatively few imagers which are found to be acceptable.
One way of using imperfect imagers in a television camera, thereby increasing the number of usable imagers and consequently lowering their cost, is to include a defect corrector in the camera. For example, U.S. patent application Ser. No. 779,862 filed on Sept. 25, 1985 in the name of Peter Alan Levine and assigned, like the present application, to RCA Corporation, relates to a defect corrector for a solid-state imager camera which includes a memory for providing data signals representative of the location of defective imager pixels and an address generator which provides data signals representative of the location of the pixel currently being read out from the imager. When an address comparator detects a match between these two data signals, a flag signal is generated which indicates the current pixel being read out from the imager is defective and corrective action is taken. The address generator and comparator have to operate at high speed which may involve high power consumption.
Since solid-state imager cameras are ideally suited for portable, i.e., battery operation, it is desirable to provide a pixel addressing generator which minimizes power consumption and the number of circuit components.